1 Field of the Invention
The invention relates to a plasma display apparatus, and more particularly to fluorescent material coated onto a fluorescent layer which is a part of the plasma display apparatus.
2 Description of the Related Art
First, hereinbelow is explained a structure of a conventional plasma display panel.
FIG. 1 is an exploded perspective view of a conventional plasma display panel.
A plasma display panel 15 is comprised of an electrically insulating front substrate 1A, and an electrically insulating rear substrate 1B facing the front substrate 1A.
The front substrate 1A is formed on a surface facing the rear substrate 1B with a scanning electrode 9 and a common electrode 10 spaced away from each other by a certain distance and extending in parallel with each other.
Each of the scanning electrode 9 and the common electrode 10 is comprised of a bus electrode 13 providing electrical conductivity, and a primary discharge electrode 2 formed on the bus electrode 3 and causing electric discharge. The primary discharge electrode 2 is composed of ITO (Indium-Tin Oxide) or SnO2 for preventing reduction in light-transmittance.
A dielectric layer 4A is formed on the front substrate 1A, covering the scanning electrode 9 and the common electrode 10 therewith. The dielectric layer 4A is covered with a protection layer 5 for protecting the dielectric layer 4A from electric discharges. The protection layer 5 is composed of magnesium oxide (MgO), for instance.
The rear substrate 1B is formed on a surface facing the front substrate 1A with a plurality of data electrodes 6 extending in a direction perpendicular to a direction in which the scanning electrode 9 and the common electrode 10 extend. The data electrodes 6 are equally spaced away from one another, and extend in parallel with one another.
A dielectric layer 4B is formed on the rear substrate 1B, covering the data electrodes 6 therewith. On the dielectric layer 4B is formed a plurality of partition walls 7 extending in parallel with the data electrodes 6. The partition walls 7 define a discharge space between the first and second substrates 1A and 1B, and the partition walls 7 located adjacent to each other define a cell therebetween.
Fluorescent material 8 is coated on sidewalls of the partition walls 7 and an exposed surface of the dielectric layer 4B. The fluorescent material 8 converts ultra-violet rays generated by discharges, into visible lights. For instance, red, green and blue (RGB) fluorescent materials are coated every three cells, ensuring displaying color images.
Discharge gas spaces sandwiched between the front and rear substrates 1A and 1B and further between adjacent partition walls 7 are filled with discharge gas comprised of helium, neon or xenon alone or in combination, for instance.
In operation, voltages each having a predetermined waveform are applied to the scanning electrode 9, the common electrode 10 and the data electrodes 6. When a voltage difference between the scanning electrode 9 and the common electrode 10 or a voltage difference between the common electrode 10 and the data electrodes 7 is over a threshold voltage, discharge is generated between the scanning electrode 9 and the common electrode 10 and between the common electrode 10 and the data electrodes 7, respectively, and accordingly, the fluorescent material 8 emits visible lights.
There have been suggested many fluorescent materials used for a plasma display panel.
For instance, Japanese Patent Application Publication No. 2002-3835 has suggested inorganic fluorescent material in which A/B is equal to or greater than 30% where A indicates a weight of particles having a diameter of 1.0 or 0.8 micrometers or smaller, and B indicates a weight of all of particles.
Japanese Patent Application Publication No. 2003-34786 has suggested spherical fluorescent material having an average diameter of 0.1 to 2.0 micrometers and a maximum diameter of 7.0 micrometers or smaller.
The inorganic fluorescent material suggested in the firstly mentioned Publication contains minute particles having a diameter of 1.0 or 0.8 micrometers or smaller by 30 weight % or greater. As a result, particles tend to be aggregated.
If particles are aggregated, the fluorescent material would have a locally increased thickness, resulting in that a voltage for generating writing-discharge is locally increased. For instance, if the fluorescent material has different thicknesses in cells, a voltage increase would occur only in cells having thick fluorescent material, and hence, display quality is degraded in the cells. Thus, uniformity in displaying images in a region in which cells are arranged, that is, a display region is not achieved.
In the secondly mentioned Publication, spherical particles are used, and the fluorescent material is designed to contain small particles much more than large particles in a particle-diameter profile for raising an arrangement density of the fluorescent material, and further for enhancing a brightness.
However, the fluorescent material suggested in the secondly mentioned Publication contain much minute particles having a diameter of 1.0 micrometer or smaller. That is, particles contained in the fluorescent material are minute on the whole. Hence, similarly to the inorganic fluorescent material suggested in the firstly mentioned Publication, the particles tend to be aggregated.
If particles are aggregated, the fluorescent material would have a locally increased thickness, resulting in that a voltage for generating writing-discharge is locally increased, similarly to the firstly mentioned Publication. Thus, uniformity in displaying images in a display region is not achieved.